1. Field of the Invention
The present invention relates to a novel hardware controlled multinode interface module for a control system. more particularly, the present invention relates to a highly distributed and highly modular interface implemented in hardware and employing a plurality of data error checking features which permit hot swapping of the interface modules on the control systems without degrading the system or causing temporary shutdown of the system.
2. Description of the Prior Art
Numerous control systems for controlling factory operations and processes are known. When such prior art control systems employed a large number of input/output controls located remotely from a central processor having racks of control equipment, individual cabling was run from the central processor racks to the input/output controls at the devices being controlled which require a large amount of system cabling. When a plurality of input/output (I/O) boards are employed and each such boards is provided with a plurality of input/output drivers and receivers each of which requires a pair of wires, the cabling for a large number of discrete I/O devices becomes the major limiting factor in a highly centralized I/O control system.
To avoid the above limitations imposed by a centralized I/O architecture, it was known to employ distributed computer architecture having individual computing systems located at remote sites and adapted to cooperate with the central host computing system and control system. Such distributed architecture systems also require an extensive amount of cabling as well as the additional expense of individual computing systems.
It has been suggested that a control system could be centralized and the commands linked to the input/output controls by local area network (LAN) techniques. Most such LAN systems requires smart controllers such as ETHERNET controllers or a smart terminal controller either of which increases the expense of the LAN systems. Most such LAN systems have a limited number of nodes which is a function of the transmission line effect and the speed of signal transmission. Typically such LAN systems have no more than 30 nodes.
Control systems which are designed to control a very large number of input/output devices and which employ a large number of nodes in a distributed system, by definition imply that the input/output devices are spread over a large area and will require large amounts of cabling. When such input/output devices are spread over a large area and include a large amount of cabling, the input/output devices and the transmission equipment are subject to industrial noise and industrial environmental conditions which generate electrical noise that in turn will produce errors and make it impossible to accurately control the input/output devices on a distributed system having a large number of nodes and a large number of input/output devices.
It would be desirable to provided a control system having a novel hardware controlled multinode interface (HCMI) which is capable of controlling more than 65,000 discrete I/O devices through approximately 256 nodes in a highly distributed architecture system such that the data required to accomplish control may be transmitted on a signal pair of conductors with associated control lines.